1. Field of the Invention
This invention relates to sheaves and is particularly directed to a sheave that is adapted to be suspended and having counter-balancing weights mounted above the sheave for maintaining the sheave in continuous alignment with a plane passing through the cable, and thereby avoiding improper wear of the rope and inefficient operation of the sheave.
2. Description of the Prior Art
At present, for such activities for lowering wire cables to which sensors and instruments are attached, as in hydrographic work from ships, a freely suspended sheave is employed. However, when the wire cable is not in the vertical plane because of towing angle, the prior art sheaves are unable to correctly lie in the plane of the line, causing undue wear on the line and the sheave, and possibly causing the cable to jump off the sheave.
The sheave assembly in allowed, copending U.S. patent application Ser. No. 222,970, filed Jan. 7, 1981, is able to avoid the above indicated malfunctioning of the sheave and wire cable by mounting counter-balancing weights above the suspended sheave or pulley. U.S. patent application Ser. No. 222,970 has the same inventor as the herein described invention and is not prior art hereto, but is described herein to better understand the problems solved by the present invention. Although the sheave of U.S. patent application Ser. No. 222,970 works very well in many situations, the use of the counterbalance weights requires a sheave assembly having an overall length that approaches twice the length of the sheave itself. Particularly with large sheaves on ships, there is frequently insufficient space to mount such a sheave assembly. Additionally, with large sheave assemblies of the type described, their weight causes them to be difficult to mount and cumbersome to handle.
U.S. Pat. No. 1,348,691 to Beaumont, discloses a counter-balanced pulley arrangement that exists in the prior art.
U.S. patent application Ser. No. 222,970 to Niskin, now allowed, is incorporated herein by specific reference thereto and is not prior art hereto.
U.S. Pat. Nos. 3,172,642; 3,132,844; 3,042,374; and 3,032,320 disclose various multiple sheave arrangements of the prior art.